Removal of gas from gas producing formations is generally accomplished by separating gas from liquids present in the formations. For example, coal bed methane is a form of natural gas that can be extracted from coal bed formations. Coal bed methane is methane gas that is contained in coal seams as a result of chemical and physical processes. Methane is adsorbed into the matrix of the coal and lines the inside pores within the coal. It is often produced at shallow depths through a bore hole that allows gas and water to be produced.
Extraction of coal bed methane is known in the prior art and generally, to extract methane, a steel encased hole is drilled into the coal seam of less than 300 to over 4,920 feet below the surface of the ground. As the pressure within the coal seam declines due to pumping of water from the coalbed, both gas and water can surface through the pump tubing. More commonly, formation water is extracted through the tubing and the isolated coal bed methane gas travels upwardly from the casing of the wellbore and is collected at the surface. The gas is generally sent to a compressor station and into natural gas pipelines. The formation or produced water is either reinjected into isolated wells, or if it does not contain contaminants, released into streams, used for irrigation, or sent to evaporation ponds. The formation water typically contains dissolved solids such as sodium bicarbonate and chloride but its chemistry will vary depending upon the geographic location of the well.
The production of coal bed methane from formations is typically characterized by a negative decline in which the gas production rate initially increases as the water is pumped off and gas begins to desorb and flow. Desorption is the process by which coals free methane when the hydrostatic pressure in the coal formation is reduced. The methane desorption process follows a curve (of gas content vs. reservoir pressure) called a Langmuir isotherm. The isotherm can be defined by a maximum gas content (at infinite pressure), and the pressure at which half that gas exists within the coal. These parameters (called the Langmuir volume and Langmuir pressure, respectively) are properties of the coal, and vary widely depending upon the physical and chemical characteristics of the coal and the geographic location. As production occurs from a coal reservoir, the changes in pressure are believed to cause changes in the porosity and permeability of the coal. This is commonly known as matrix shrinkage/swelling.
Many coal bed methane producing formations have been drilled and abandoned or drilled and shut in, leaving orphaned wells that still possess gas pressure. As an alternative to the pumping of water off of the coals to produce gas or plugging and reclaiming wells, the current isolation provides an apparatus and method for continued recovery of coal bed methane from coal bed methane formations without releasing or removing formation water. In addition, there are many shallow gas wells which produce gas from rock types other than coal in which the hydrostatic head of the produced water is greater than the gas bearing formations reservoir pressure. The current apparatus will also allow gas to be produced in these formations and wells. In accordance with the disclosure, there is provided a downhole isolation tool for introduction within a casing of a gas formation, having an upper open end for reception of a tubing assembly, the tool comprising a circumferential multi-part housing with the upper open end; the housing having an internal cavity for insertion of a perforated cylindrical internal tool, a wire mesh screen, a sleeve member; and a perforated bore tail.